Building foundation structure formed with soil improving body and raft foundation and construction method for soil improvement and raft foundation

ABSTRACT

To provide building foundation structure formed with a soil improving body and raft foundation that can suppress weight increase of a soil improving body while achieving suppression of differential settlement and improvement of bearing capacity of the whole foundation and that can be applied to medium-rise buildings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to building foundation structure formed with a soil improving body that improves soft soil or soil in which liquefaction occurrence is foreseen at the time of earthquakes and raft foundation cast on the soil improving body and a construction method for soil improvement and raft foundation.

2. Description of the Background Art

As a foundation for a building for soft soil or soil with possible liquefaction occurrence at the time of earthquakes, Japanese Unexamined Patent Publication No. 61-5114 (FIG. 1 and FIG. 2) discloses increasing rigidity as the whole soil and preventing damage to structure by liquefaction of the soil by penetrating into and drawing out of a soil while rotating an agitation blade of a deep mixing soil stabilizer, supplying an agglomeration chemical to discharge to the vicinity of the agitation blade at the time of penetration, agitating and mixing in the soil and allowing the agglomeration chemical to solidify, and forming a underground wall made up of lattice-like or other-shape soil improving bodies (Patent Document 1). Japanese Unexamined Patent Publication No. 2000-291022 (FIG. 1, FIG. 8 and FIG. 9) discloses reducing a mean settlement amount and a differential settlement amount of foundation by piled raft foundation which uses spread foundation in combination with pile foundation, formed by placing concrete piles beneath spread foundation such as continuous footing or raft foundation (Patent Document 2). Japanese Patent No. 3608568 (FIG. 1 and FIG. 2) discloses suppressing differential settlement and suppressing a lateral flow of unimproved soil at the level of the lower part of the soil improving body while reducing the weight of a soil improving body, by the soil improving body formed by improving the subsurface layer of soft soil, which has a horizontal plate form top improving body, periphery improving bodies suspended from the bottom surface of the top improving body and forming outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas, as well as raft foundation cast on the soil improving body (Patent Document 3).

SUMMARY OF THE INVENTION

In the foundation by the underground wall made up of soil improving bodies of Patent Document 1, columnar soil improving bodies need to be continuously produced to form a wall, and therefore, it takes time to build the soil improving bodies and at the same time the cost increases.

In addition, in the piled raft foundation as is the case of Patent Document 2, a large number of reinforced concrete piles need to be placed beneath the foundation by the use of large heavy machinery, and as compared to the case in which the soil beneath the foundation is improved, the weight increases and at the same time the cost increases.

As against these, in the configuration having soil improving bodies formed by improving soft soil into shallow-layer soil and raft foundation cast on the soil improving bodies of Patent Document 3, as compared to the foundations of Patent Documents 1 and 2, the foundation is lightweight and at the same time easy to construct, and is therefore suited for the foundation structure for buildings which have comparatively small loads and large building area.

However, the foundation structure of buildings having the soil improving bodies and raft foundation of Patent Document 3 may be sometimes unable to achieve necessary bearing capacity and thereby unable to be used for the foundation of, for example, medium-rise reinforced concrete buildings of 5 to 7 stories. The foundation structure is susceptible to improvement in order to provide bearing capacity necessary for medium-rise buildings and render itself applicable to such buildings.

What the present invention aims at solving in view of the foregoing conditions is to provide building foundation structure formed with soil improving bodies and raft foundation and construction method for soil improvement and raft foundation that can suppress weight increase of soil improving bodies while achieving suppression of differential settlement and improvement of bearing capacity of the overall foundation, achieve high comparative economy, and are applicable also to medium-rise buildings.

In order to solve the above problems, the present invention provides building foundation structure formed with soil improving bodies and raft foundation that includes a shallow-layer soil improving body that improves the subsurface of soft soil or soil with possible liquefaction occurrence, which is formed by a horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas, a peristyle-form soil improving body including a plurality of columnar improving bodies that improve the soil, which are suspended from the bottom surface of the periphery improving bodies and the internal improving body or suspended and provided in a row from the bottom surface of a plate in contact with the bottom surfaces of the periphery improving bodies and the internal improving body or the bottom surface of an intermediate in contact with the bottom surface of the plate, and a raft foundation cast on the top improving body of the shallow-layer soil improving body.

It is preferable that the peristyle-form soil improving body comprises columnar improving bodies disposed immediately beneath columns of a building to be constructed on the raft foundation and columnar improving bodies provided in a row immediately beneath underground beams.

Furthermore, it is preferable that covered cylindrical cap materials are fitted over to the top end of the columnar improving body.

In order to solve the above problems, the present invention provides a construction method for soil improvement and raft foundation that includes the steps of digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body, forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in the form of the columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating, forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting, and building a raft foundation of reinforced concrete construction on the top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises: the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; and the peristyle-form soil improving body including a plurality of the columnar improving bodies suspended and provided in a row from the bottom surfaces of the periphery improving bodies and the internal improving body.

In order to solve the above problems, the present invention provides a construction method for soil improvement and raft foundation that includes the steps of digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body, forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in the form of the columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating, mounting a plate or an intermediate as well as the plate on the top end surface of the peristyle-form soil improving body, forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting, and building a raft foundation of reinforced concrete construction on the top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises: the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; and the peristyle-form soil improving body including a plurality of the columnar improving bodies that are suspended and provided in a row from the bottom surface of the plate in contact with the bottom surfaces of the periphery improving bodies and the internal improving body or the bottom surface of the intermediate in contact with the bottom surface of the plate.

The building foundation structure formed with the soil improving body and raft foundation of the present invention has: a shallow-layer soil improving body that improves the subsurface of soft soil or soil with possible liquefaction occurrence, which is formed by a horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; a peristyle-form soil improving body including a plurality of columnar improving bodies that improve the soil, which are suspended from the bottom surface of the periphery improving bodies and the internal improving body or suspended and provided in a row from the bottom surface of a plate in contact with bottom surfaces of the periphery improving bodies and the internal improving body or the bottom surface of an intermediate in contact with the bottom surface of the plate; and a raft foundation cast on the top improving body of the shallow-layer soil improving body. Therefore, differential settlement can be suppressed and a lateral flow of unimproved soil at the level of the soil improving body lower part can be suppressed, while reducing the weight of the soil improving body as compared to the case in which overall foundation bottom part is improved.

In addition, the building load is supported by the frictional force (circumferential frictional force) of the side surface and reaction force (tip reaction force) of the bottom end surface of columnar soil improving bodies that make up a peristyle-form soil improving body and large bearing capacity is able to be obtained. Therefore, the present invention can be used for foundation of medium-rise buildings.

Furthermore, locations of the columnar improving bodies, the pitch between adjacent columnar improving bodies and diameter and length of the columnar improving bodies can be varied to easily change the circumferential surface frictional force and tip reaction force. The present invention can be used for buildings of various shapes and loads by optimizing the cost while securing performance by controlling sharing ratio of soil contact reaction force, circumferential surface frictional force, and tip reaction force and relative settlement rate.

In addition, columnar improving bodies that make up a peristyle-form soil improving body are not allowed to be suspended from the bottom surface of the top improving body but allowed to be suspended from the bottom surfaces of comparatively thick periphery improving bodies and internal improving body. It is therefore possible to efficiently increase the bearing capacity for buildings while suppressing an increase of the number of columnar improving bodies.

In addition, as compared to the configuration to form an underground wall made up of lattice-like or other-shape soil improving bodies, the present invention avoids the need of continuously forming columnar improving bodies to form a wall and can shorten the construction period and at the same time can reduce weight and cost.

Furthermore, as compared to the piled raft foundation, the present invention is not of a structure to place a large number of reinforced concrete piles beneath the foundation by the use of large heavy machinery. It is therefore possible to reduce the construction period and at the same time to reduce weight and cost.

Furthermore, according to the configuration to arrange plate material or plate material and intermediate between the periphery improving bodies as well as the internal improving body and columnar improving bodies, the top surface of the columnar improving bodies that make up the peristyle-form soil improving body and the bottom surfaces of the periphery improving bodies and the internal improving body that make up the shallow-layer soil improving body can be easily deviated relatively in the horizontal direction at the time of earthquakes. It is therefore possible to reduce the seismic force (horizontal force) transmitted to buildings constructed on the relevant foundation structure and to greatly reduce the shakiness. Consequently, earthquake-resistant performance of the overall structure including the relevant foundation structure and buildings constructed on the structure can be still more improved.

In addition, the peristyle-form soil improving body is configured with columnar improving bodies disposed immediately beneath columns of a building to be built on the raft foundation and columnar improving bodies provided in a row immediately beneath underground beams. Then, in addition to the above-mentioned effects, the strength and the rigidity of the overall foundation are improved and the bearing capacity for the building is further increased.

Furthermore, when a covered-cylindrical cap material is fitted over the top end part of the columnar improving body, in addition to the above-mentioned effect, the plate material (cover portion of the cap material) will not come off from the columnar improving body top end surface by earthquakes, and the seismic isolation reliability described above can be secured over a long period of time.

The construction method for soil improvement and raft foundation related to the present invention includes steps of digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body, forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in a form of the columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating, forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting, and building a raft foundation of reinforced concrete construction on a top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises: the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; and the peristyle-form soil improving body including a plurality of columnar improving bodies suspended and provided in a row from the bottom surfaces of the periphery improving bodies and the internal improving body. The present invention is, therefore, able to suppress differential settlement and suppress a lateral flow of unimproved soil at the level of the soil improving body lower part while reducing the weight of the soil improving body as compared to the case in which the overall foundation lower part has soil improved.

In addition, as compared to the configuration to form an underground wall made up of lattice-like or other-shape soil improving bodies, the present invention avoids the need of continuously forming columnar improving bodies to form a wall and can shorten the construction period and at the same time can reduce weight and cost.

Furthermore, as compared to the piled raft foundation, the present invention is not of a structure to place a large number of reinforced concrete piles beneath the foundation by the use of large heavy machinery. It is therefore possible to reduce the construction period and at the same time to reduce weight and cost.

In addition, according to the building foundation structure formed with soil improving bodies and raft foundation obtained by the construction method for soil improvement and raft foundation of the present invention, the building load is supported by the frictional force of the side surface and reaction force of the bottom end surface of columnar soil improving bodies that make up a peristyle-form soil improving body in addition to the soil reaction force of the shallow-layer soil improving body and large bearing capacity is able to be obtained. Therefore, the present invention is able to be used for foundation of medium-rise buildings.

Furthermore, according to the building foundation structure formed with soil improving bodies and raft foundation obtained by the construction method for soil improvement and raft foundation of the present invention, locations of columnar improving bodies, the pitch between adjacent columnar improving bodies and diameter and length of columnar improving bodies can be varied to easily change the circumferential surface frictional force and tip reaction force. The present invention is able to be used for buildings of various shapes and loads by optimizing the cost while securing performance by controlling sharing ratio of soil contact reaction force, circumferential surface frictional force, and tip reaction force and relative settlement rate.

Still more, according to the building foundation structure formed with soil improving bodies and raft foundation obtained by the construction method for soil improvement and raft foundation of the present invention, columnar improving bodies that make up a peristyle-form soil improving body are not allowed to be suspended from the bottom surface of the top improving body but allowed to be suspended from the bottom surfaces of comparatively thick periphery improving bodies and internal improving body. It is therefore possible to efficiently increase the bearing capacity for buildings while suppressing an increase of the number of columnar improving bodies.

The construction method for soil improvement and raft foundation of the present invention includes steps of digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body, forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in a form of the columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating, mounting a plate or an intermediate as well as the plate on the top end surface of the peristyle-form soil improving body, forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting, and building a raft foundation of reinforced concrete construction on a top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas, and the peristyle-form soil improving body including a plurality of the columnar improving bodies that are suspended and provided in a row from the bottom surface of the plate in contact with the bottom surfaces of the periphery improving bodies and the internal improving body or the bottom surface of the intermediate in contact with the bottom surface of the plate. Therefore, in addition to the effects of the above-mentioned construction method for soil improvement and raft foundation, in the building foundation structure formed with soil improving bodies and raft foundation obtained by the construction method for soil improvement and raft foundation related to the present invention, plate material or plate material and intermediate are arranged between the periphery improving bodies as well as the internal improving body and columnar improving bodies. Consequently, the top surface of the columnar improving bodies that make up the peristyle-form soil improving body and the bottom surfaces of the periphery improving bodies and the internal improving body that make up the shallow-layer soil improving body are able to be easily deviated relatively in the horizontal direction at the time of earthquakes. It is therefore possible to reduce the seismic force (horizontal force) transmitted to buildings constructed on the relevant foundation structure and to greatly reduce the shakiness. Consequently, earthquake-resistant performance of the overall structure including the relevant foundation structure and buildings constructed on the structure can be still more improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a building foundation structure formed with soil improving bodies and raft foundation according to one embodiment of the present invention, FIG. 1( a) is a plan view and FIG. 1( b) is a cross-sectional view on arrow A-A of FIG. 1( a);

FIG. 2 is an enlarged plan view of a principal part;

FIG. 3 is an enlarged longitudinal sectional view of a principal part;

FIG. 4 is an enlarged longitudinal sectional view of a principal part;

FIG. 5 is an illustration showing soil reaction force of a shallow-layer soil improving body as well as frictional force of the side surface and reaction force of the bottom end surface of peristyle-form soil improving body; and

FIG. 6 is a schematic view showing a configuration with plate material interposed between a columnar improving body and a periphery improving body as well as an internal improving body, and FIG. 6( a) is an enlarged longitudinal cross-sectional view of a principal part and FIG. 6( b) is a fragmentary cross-sectional view in perspective of a covered cylindrical cap material.

DETAILED DESCRIPTION OF THE INVENTION

A building foundation structure formed with soil improving bodies and raft foundation related to the present invention uses both a shallow-layer soil improving body and peristyle-form soil improving body which improve soft soil or soil from which liquefaction occurrence is foreseen, and is formed by placing raft foundation on the shallow-layer soil improving body. Referring to drawings, embodiments that put the present invention into effect will be described. In the following embodiments, the case in which the soil is soft soil will be discussed as examples.

FIG. 1 to FIG. 3 are schematic views of building foundation structure formed with soil improving bodies and raft foundation related to one embodiment of the present invention. FIG. 1( a) is a plan view, FIG. 1( b) a cross-sectional view on arrow A-A of FIG. 1( a), FIG. 2 an enlarged plan view of a principal part, and FIG. 3 an enlarged longitudinal sectional view of a principal part.

As shown in FIG. 1 to FIG. 3, a shallow-layer soil improving body 1 is formed by a horizontal plate form top improving body 6 that is rectangular in a plan view, periphery improving bodies 7, 7 and 8, 8 that are suspended from the bottom surface of the top improving body 6 and form rectangular outer frames in a plan view, and internal improving bodies 9, 9 and 10, 10, that are suspended from the bottom surface of the top improving body 6, link across the outer frames, and partition an area inside the periphery improving bodies enclosed by the outer frames into a plurality of areas.

The planar shape of the top improving body and the periphery improving body may be an outer shape formed by linking a plurality of rectangles, and the planar shapes of the top improving body and the periphery improving body need not be same. In addition, the internal improving body is of a shape combining the periphery improving body and the internal improving body including the parallel crosses as viewed two-dimensionally as shown in FIG. 1( a), and may include two-cell by one-cell or two-cell by two-cell rectangle as viewed two-dimensionally, and a suitable number is chosen to partition the area inside the periphery improving body into a plurality of areas in conformity to the outer shape of the periphery improving body.

In addition, a peristyle-form soil improving body 2 is suspended and provided in a row from the bottom surfaces of the periphery improving bodies 7, 7 and 8, 8 as well as the internal improving bodies 9, 9 and 10, 10 of the shallow-layer soil improving body 1 as shown in FIG. 1 and are formed by a plurality of columnar improving bodies 11, . . . which are stopped in the midway of soft soil S (for example, soil with an extremely small N value over the depth of about 20 m) and are not fixed to the support layer.

In FIG. 1( a), pitches Px1, Px2, Px3, Py1, Py2, and Py3 between curbs of shallow-layer soil improving body 1 are installed in a range, for example, from 5 to 20 meters and pitches Qx and Qy between adjacent columnar improving bodies 11, 11 are set to, for example, about 2 to 4 meters.

In addition, in FIG. 3, the thickness of raft foundation 3 is set to about 0.2 to 0.4 meters, the maximum thickness C1 of top improving body 6 is set to about 0.6 to 1.2 meters, and the thickness C2 of periphery improving bodies 7, 7 and 8, 8 as well as the thickness C3 of internal improving bodies 9, 9 and 10, 10 are set to about 1 to 2 meters, but the thickness C2 may not be the same with the thickness C3 and for example, the thickness C2 may be made thicker than that of C3.

Furthermore, the width B1 of periphery improving bodies 7, 7 and 8, 8 and the width B2 of internal improving bodies 9, 9 and 10, 10 are set to about 3 to 4 meters, but the width B1 may not be the same with the width B2 and for example, the width B1 may be made thicker than the width B2.

Furthermore, the diameter D of columnar improving bodies 11, . . . is set to about 0.6 to 1 meter and the length (depth) L is set to about 5 to 7 meters, but the diameter D and the length L may be suitably varied in accord with locations. For example, in FIG. 1, it is easy to vary the diameter D and length L of columnar improving bodies 11, . . . beneath poles 5, . . . and the diameter D and length L of columnar improving bodies 11, . . . beneath underground beams 4 (see FIG. 3) as well as the pitches Qx and Qy between adjacent columnar improving bodies 11, 11 in accord with locations, and by doing like this, the load sharing ratio and the relative settlement rate may be controlled to achieve desired values.

Next discussion will be made on the construction method for building the soil improving body having the shallow-layer soil improving body 1 and peristyle-form soil improving body 2.

In the shallow-layer soil improving body 1 and the peristyle-form soil improving body 2 shown in FIG. 1( b) and FIG. 3, first of all, the subsurface on the downside from the soil level GL of soft soil S is dug down in a form of the shallow-layer soil improving body 1 by, for example, spading by backhoe.

Then, by the use of construction machinery such as small pile driver, a peristyle-form soil improving body 2 is formed by agitating while injecting a solidification material such as cement based solidification material and water after excavating the soft soil S in the form of the columnar improving bodies 11, . . . . Or the peristyle-form soil improving body 2 is formed by adding and mixing a solidification material to soil taken by excavating the soft soil S in the form of columnar improving bodies 11, . . . and backfilling, and compacting after mixing and agitating.

Then, the shallow-layer soil improving body 1 is formed by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body 1 and backfilling and screeding, and compacting by heavy machinery, rollers, etc.

The soil improving body constructed in this way is able to be applied even when the soft soil layer S is extremely deep and does not give rise to the lift-up of buildings because the soil improving body is drawn down together with surrounding soil subsidence.

Furthermore, on the top soil improving body 6 of the shallow-layer soil improving body 1, the raft foundation 3 of reinforced concrete construction is built. In the raft foundation 3, underground beams 4 of reinforced concrete construction having the shape two-dimensionally same as that of periphery improving bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10 of the shallow-layer soil improving body 1 are formed integral with the raft foundation 3. Furthermore, columns 5, . . . are disposed upright at the predetermined location of the underground beams 4.

The raft foundation 3, underground beams 4 and columns 5, . . . are built on the top soil improving body 6 by setting base plates, anchor bolts, etc. of the columns 5, . . . , placing reinforcing bars in the raft foundation 3 and underground beams 4, casting concrete for the raft foundation 3 and underground beams 4, and then, building columns 5, . . . . By this kind of configuration, even when non-uniform load of structure above the foundation is exerted to the raft foundation 3, the shallow-layer soil improving body 1 and the raft foundation 3 move in concert and the load is distributed to achieve nearly uniform load to the soft soil layer directly beneath, which is the principal cause of settlement, and differential settlement can be thereby suppressed.

FIG. 4 is a longitudinal sectional view showing an example in which an engaging protrusion 3 a to the shallow-layer soil improving body 1 is installed to the bottom surface of the raft foundation 3. The engaging protrusion 3 a is formed continuously or intermittently on the bottom surface of the raft foundation 3 at locations corresponding to periphery improving bodies 7,7 and 8, 8 and internal improving bodies 9, 9 and 10, 10 of the soil improving body 1. In addition, on the top surface of the shallow-layer soil improving body 1, engaging depressions (7 a, 8 a, 9 a, and 10 a, and engaging depressions 8 a and 10 a are shown in FIG. 4) that engage the engaging protrusion 3 a are formed. These engaging depressions can be formed by assembling formwork at places where the engaging depressions (8 a, 10 a, etc.) are formed when the shallow-layer soil improving body 1 is formed. By the way, the reason why engaging depressions are formed at the top part of the periphery improving bodies 7, 7 and 8, 8 as well as the internal improving bodies 9, 9 and 10, 10 of the shallow-layer soil improving body 1 is to prevent lowering of rigidity and strength of the shallow-layer soil improving body 1 when portions with reduced thickness may be formed in the shallow-layer soil improving body 1. Engaging the engaging protrusion 3 a on the bottom surface of the raft foundation 3 with the engaging depression on the top surface of the shallow-layer soil improving body 1 can increase unity of the raft foundation 3 with the shallow-layer soil improving body 1 as well as rigidity and strength of the overall foundation. Consequently, the differential settlement suppression effect can be still more increased.

According to the building foundation structure formed with the foregoing shallow-layer soil improving body 1, the peristyle-form soil improving body 2, and raft foundation 3, as compared to the case of improving the soil for the overall foundation bottom, differential settlement and a lateral flow of unimproved soil at the level of the lower part of the soil improving body can be suppressed while reducing the weight of the soil improving body.

In addition, because the weight of the building is supported by the frictional force (circumferential frictional force) F2, . . . of the side surface (circumferential surface) of the columnar improving bodies 11, . . . that make up the peristyle-form soil improving body 2 and the reaction force (tip reaction force) F3, . . . of the bottom end surface, in addition to the soil reaction force (contact soil reaction force) F1 of the shallow-layer soil improving body 1 shown in FIG. 5, large bearing capacity can be obtained and increased foundation soil bearing capacity and suppressed settlement can be achieved. The building foundation structure can be used as the foundation for medium-rise buildings (reinforced concrete structure).

Furthermore, as described above, by varying the locations of columnar improving bodies 11, . . . , the pitches Qx and Qy between adjacent columnar improving bodies 11 and 11, as well as the diameter D and length L of columnar improving bodies 11, . . . , the circumferential frictional force F2 and the tip reaction force F3 can be easily varied. It is therefore possible to use the building foundation structure formed with the shallow-layer soil improving body 1, peristyle-form soil improving body 2, and raft foundation 3 according to the present invention can be used for buildings of various shapes and loads with the cost optimized while securing the performance by controlling the bearing ratio of contact reaction force F1, circumferential frictional force F2, and tip reaction force F3 and the relative settlement rate.

Furthermore, because columnar improving bodies 11, . . . that make up the peristyle-form soil improving body 2 are not allowed to be suspended from the bottom surface of the top improving body 6 but allowed to be suspended from bottom surfaces of comparatively thick periphery improving bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10, it is possible to efficiently increase the bearing capacity for buildings while suppressing an increase of the number of columnar improving bodies 11. In particular, configuring the peristyle-form soil improving body 2 with columnar improving bodies 11, . . . disposed beneath columns 5, . . . of a building to be constructed on the raft foundation 3 and columnar improving bodies 11, . . . provided in a row beneath underground beams 4 can further improve the strength and the rigidity of the overall foundation and can still more increase the bearing capacity.

Furthermore, in the case that the building foundation structure formed with the shallow-layer soil improving body 1, peristyle-form soil improving body 2, and raft foundation 3 is used for the soil in which liquefaction occurrence is foreseen, the soil under the building is partitioned and bound by the peristyle-form soil improving body 2 and is therefore stabilized, and the liquefaction resistance can be markedly increased.

Furthermore, even in the case of the soil in which consolidation lowering is foreseen, installing the peristyle-form soil improving body 2 can suppress differential settlement still more efficiently than in the case of the shallow-layer soil improving body 1 only.

In addition, as compared to the configuration to form an underground wall made up of lattice-like or other-shape soil improving bodies, the present invention avoids the need of continuously forming columnar improving bodies to form a wall and can therefore shorten the construction period and at the same time can reduce weight and cost.

Furthermore, as compared to the piled raft foundation, the present invention is not of a structure to place a large number of reinforced concrete piles beneath the foundation by the use of large heavy machinery. It is therefore possible to reduce the construction period and at the same time to reduce weight and cost.

FIG. 6 shows a configuration with plate materials interposed between columnar improving bodies 11, . . . and periphery improving bodies 7, 7 and 8, 8 as well as internal improving bodies 9, 9 and 10, 10 so that the top end surfaces of the columnar improving bodies 11, . . . do not come directly in contact with the bottom surfaces of the periphery improving bodies 7, 7 and 8, 8 and the internal improving bodies 9, 9 and 10, 10, unlike the configuration in which the columnar improving bodies 11, . . . are suspended from the bottom surfaces of periphery improving bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10 as shown in FIG. 1( b), FIG. 3 and FIG. 4. FIG. 6( a) is an enlarged longitudinal cross-sectional view of a principal part and FIG. 6( b) is a fragmentary cross-sectional view in perspective of a covered cylindrical cap material 12 including the plate material.

That is, in the configuration shown in FIG. 6, after forming each of the columnar improving bodies 11, . . . which make up the peristyle-form soil improving body 2, on the top end part of these columnar improving bodies 11, . . . , covered cylindrical cap materials 12, . . . are fitted over, and on these cap material 12, . . . , a shallow-layer soil improving body 1 is constructed.

Consequently, the columnar improving bodies 11, . . . are suspended from the bottom surface of the plate material (disk-form cover 12A of cap material 12), which comes in contact with the bottom surfaces of the periphery improving bodies 7, 7 and 8, 8 and the internal improving bodies 9, 9 and 10, 10.

The cap material 12 is composed with a disk-shape cover 12A which is plate material interposed between columnar improving bodies 11, . . . and periphery improving bodies 7, 7 and 8, 8 as well as internal improving bodies 9, 9 and 10, 10 and annular cylinder 12B attached to the side surface of columnar improving bodies 11, . . . , with the top end surface of each of columnar improving bodies 11, . . . , the bottom surface 12 a of the cover 12A comes in contact, and with the top end side surface of each of the columnar improving bodies 11, . . . , the inner side surface 12 b of the cylinder 12B comes in contact. The cap material 12, . . . may be freely fitted to the top end part of columnar improving bodies 11, . . . in such a manner that a clearance is provided between the top end side surface of columnar improving bodies 11, . . . and the inner side surface of 12 b of the cylinder 12B.

In addition, on the bottom side of the plate material (for example, the cover 12A), another plate material or intermediates such as level mortar may be disposed. For example, on the lower side of the plate material, a single or a plurality of different plate material may be disposed, below which level mortar, etc. may be arranged.

The plate material is preferably, fluororesin such as polytetrafuluoroethylene (tetrafluoride), etc. or polyacetal, polypropylene, polyethylene terephthalate, nylon, or ABS and other synthetic resin, or stainless steel or aluminum alloys and other metals, or metals to the surfaces of which fluororesin, etc. are coated, and it is preferable to achieve small frictional coefficient.

According to the configuration to arrange plate material (disk-shape cover 12A of cap material 12) or plate material and intermediate which comes in contact with the bottom surface of the plate material between columnar improving bodies 11, . . . and periphery improving bodies 7, 7 and 8, 8 as well as internal improving bodies 9, 9 and 10, 10, except the cap material 12, the configuration is exactly the same as that of FIG. 1 to FIG. 5, and thus the working-effects by the configuration of FIG. 1 to FIG. 5 are achieved. In addition to the working effects, the top surface of the columnar improving bodies 11, . . . that make up the peristyle-form soil improving body 2 and the bottom surfaces of periphery improving bodies 7, 7 and 8, 8 as well as internal improving bodies 9, 9 and 10, 10 that make up the shallow-layer soil improving body 1 can be easily deviated (deviated relatively in the horizontal direction) at the time of earthquakes. It is therefore possible to reduce the seismic force (horizontal force) transmitted to buildings constructed on the relevant foundation structure and to greatly reduce the shakiness. Consequently, earthquake-resistant performance of the overall structure including the building foundation structure and buildings constructed on the structure as shown in FIG. 6 can be still more improved.

The example shown in FIG. 6 is the configuration in which the covered cylindrical cap materials 12, . . . are fitted over the top end of columnar improving bodies 11, . . . , but the cap material may not be a covered cylindrical cap material of this kind but, for example, may be a covered polygonal cylindrical cap material such as covered rectangular cylindrical shape. Alternatively, between columnar improving bodies 11, . . . and periphery improving bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10, for example, plate materials may be interposed, and therefore, disk or polygonal plate, or other plate material alone may be used. However, according to the configuration in which a covered-cylindrical cap material is fitted over top end parts of columnar improving bodies 11, . . . , the plate material (disk-shape cover 12A in the example of FIG. 6) will not come off from top end surfaces of columnar improving bodies 11, . . . by earthquakes, and the performance can be continuously exhibited over a long period of time, and it is therefore a more preferable embodiment.

In addition, in the configuration in which another plate material or intermediates such as level mortar are arranged on the downside of the plate material, the relative move in the horizontal direction of the top surface of columnar improving body 11 that composes the peristyle-form soil improving body 2 with respect to the bottom surface of periphery improving bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10 that compose the shallow-layer soil improving body 1 can be made still more stable and still more reliable at the time of earthquakes. 

1. A building foundation structure, comprising: a shallow-layer soil improving body that improves the subsurface of soft soil or soil with possible liquefaction occurrence, which is formed by a horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; a peristyle-form soil improving body including a plurality of columnar improving bodies that improve the soil, which are suspended from the bottom surface of the periphery improving bodies and the internal improving body or suspended and provided in a row from the bottom surface of a plate in contact with bottom surfaces of the periphery improving bodies and internal improving body or the bottom surface of an intermediate in contact with the bottom surface of the plate; and a raft foundation cast on the top improving body of the shallow-layer soil improving body.
 2. The building foundation structure according to claim 1, wherein the peristyle-form soil improving body comprises columnar improving bodies disposed immediately beneath columns of a building to be constructed on the raft foundation and columnar improving bodies provided in a row immediately beneath underground beams.
 3. The building foundation structure according to claim 1, wherein covered cylindrical cap materials are fitted over to the top end part of the columnar improving body.
 4. A construction method for soil improvement and raft foundation, comprising the steps of: digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body; forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in a form of columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating; forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting; and building a raft foundation of reinforced concrete construction on a top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises: the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; and the peristyle-form soil improving body including a plurality of the columnar improving bodies suspended and provided in a row from the bottom surfaces of the periphery improving bodies and the internal improving body.
 5. A construction method for soil improvement and raft foundation, comprising the steps of: digging down the subsurface of soft soil or soil with possible liquefaction occurrence in a form of a shallow-layer soil improving body of a soil improving body; forming a peristyle-form soil improving body by agitating while injecting a solidification material and water after excavating the soil in a form of the columnar improving bodies, or by adding and mixing a solidification material to soil taken by excavating the soil in the form of the columnar improving bodies and backfilling, and compacting after mixing and agitating; mounting a plate or an intermediate as well as the plate on the top end surface of the peristyle-form soil improving body; forming the shallow-layer soil improving body by adding and mixing a solidification material to the soil taken by excavating the soil in the form of the shallow-layer soil improving body and backfilling and screeding, and compacting; and building a raft foundation of reinforced concrete construction on a top improving body of the shallow-layer soil improving body, wherein the soil improving body comprises: the shallow-layer soil improving body that is formed by the horizontal plate form top improving body, periphery improving bodies that are suspended from the bottom surface of the top improving body and form outer frames, and at least one internal improving body that is suspended from the bottom surface of the top improving body, at the same time links across the outer frames, and partitions an area inside the periphery improving bodies into a plurality of areas; and the peristyle-form soil improving body improving a plurality of the columnar improving bodies that are suspended and provided in a row from the bottom surface of the plate in contact with the bottom surfaces of the periphery improving bodies and the internal improving body or the bottom surface of the intermediate in contact with the bottom surface of the plate. 